One of the pieces of information we want to encode in the QR code for secondary devices attempting to log-in is an ephemeral AES-256 key. We already have utils written for generating the key on both `web` and `native` by @bartek I believe, so I just made the calls and encoded the key into the QR code.
The device ID generation/encoding process will be the next step in the diff, so for now it's just going to be the same placeholder string as before.
Addresses [[ https://linear.app/comm/issue/ENG-4797/generate-an-aes256-key-ephemeral-for-the-secondary-device | ENG-4797 ]].